Although significant progress has been made in the area of protein sorting and establishment of polarity in other systems, little is known about the molecular mechanisms underlying these events in the RPE. Due to the participation of the RPE in a variety of retinal diseases, such as diabetic retinal detachment and macular degeneration, the elucidation of mechanisms involved in establishing and maintaining the polarity of the RPE constitutes an important goal in retinal research. Protein sorting in RPE differs in several ways from other transporting epithelia. Direct comparisons of sorting events in the well characterized MDCK model versus RPE provides an ideal system in which to study the role of various potential cytoplasmic regulators in the establishment and maintenance of polarity in epithelial cells of diverse origin. The roles of the TGN and microtubule-dependent motors in protein sorting and transport in RPE will be examined by fluorescent video microscopy of cells containing GFP-tagged apically and basolaterally targeted proteins, antibody microinjection and in vitro vesicle budding and surface targeting assays. Many of the experimental tools to be used in this study, including the polarized cell line, RPE- J, have been developed in our lab.